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In Jamaica, I ate an unusual fruit called ackee, which I understand is banned in the United States because it is toxic. The locals told me it’s OK if prepared properly. What’s the deal? Ackee is the name of an evergreen tree native to West Africa but common in the Caribbean, and the name of its fruit. The fruits are pear-shaped and bright red or orange when ripe. Inside are three large black seeds surrounded by a white pulp that can, if prepared with care, be eaten. Jamaica is the place to go if you want to try this. Ackee is the national fruit, and ackee and saltfish is the national dish. The fruit is rich in essential fatty acids as well as protein, vitamin A, and zinc. The catch is that it’s also rich in the toxic substances hypoglycin A and B. To avoid dying, make sure ackee ripens properly, and take only the inner yellow fleshy part, discarding the black seeds and any red parts. Then, clean and wash the fruit, boil it in water, and throw the water out, because it will contain the poison. What’s left can be cooked and eaten. I actually had it once in elementary school. The parents of a Jamaican child brought it in as a show-and-tell. It looked a bit like scrambled eggs, and I have to admit I couldn’t make out much of a taste past the saltfish that was mixed in. But I would happily try it again. The biochemistry of the poisons is interesting. They kill by a sort of hypoglycemia (low blood sugar). Normally, as you use up the glucose in your blood, your liver releases glucose that it stores in the form of glycogen. The toxins stop this process, so that a few hours after ingesting them, your blood glucose crashes, leaving you hypoglycemic, vomiting, convulsing, and possibly dead. While the importation of ackee fruits is forbidden by the United States, you can buy canned, prepared ackee, which should be safe to eat. Bon appetit (if you’re up for it!) Ask Dr. Knowledge is written by Northeastern University physicist John Swain. E-mail questions to drknowledge@globe.com or write to Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.